Laser scanning units are known comprising a laser diode for generating a laser beam, a rotating polygonal mirror for reflecting the laser beam along a scan line on a photoconductive (PC) drum, and post scan optics comprising at least one fΘ lens positioned between the rotating mirror and the PC drum. Ghosting light may be generated by reflection of the laser beam at a surface of a lens forming part of the post-scan optics. The ghosting light may be re-reflected off the polygonal mirror toward the PC drum, thereby causing print defects. A shield covering at least a portion of the polygonal mirror is provided so as to block the ghosting light.
U.S. Pat. No. 5,901,000 discloses a shroud provided about a rotatable polygonal mirror. The shroud forms part of a cover, which also includes a rib functioning to cancel noise generated during rotation of the mirror.
There is a need for reducing or blocking ghosting light generated in a laser scanner unit having a single polygonal mirror reflecting a plurality of laser beams impinging upon the mirror and further including opposing post-scan optical assemblies.